As an impedance matching circuit of this sort, a SAW (surface acoustic wave) filter, for example, is used in a transmitting/receiving circuit of mobile communications such as a portable phone and radio LAN. The SAW filter enables one to set electric power of a signal to be transmitted to the maximum and to set noise of a received signal to the minimum and also enables one to preset a predetermined bandwidth by matching input/output impedance of an amplifier such as a LNA (low noise amplifier) and a PA (power amplifier) with predetermined characteristic impedance, e.g., 50 Ω.
By the way, while an ASIC (application specific integrated circuit) composing a plurality of circuits such as an RF (radio frequency) circuit and a digital signal processing circuit is used lately as the transmitting/receiving circuit described above, it is desired to configure the function of the SAW filter described above on the ASIC to realize SoC (System On a Chip) in which the whole system is configured on one chip in order to downsize and to reduce the cost of the mobile communication terminals.
Then, as shown in FIG. 17, there has been proposed an impedance matching circuit 60 which is composed of a concentrated constant element in which a plurality of spiral inductors 62 are connected and which may be configured on the ASIC as disclosed in, for example, Masayoshi Aikawa, et. al., “Monolithic Microwave Integrated Circuit (MMIC)”, Second Edition, The Institute of Electronics, Information and Communication Engineers, May 20, 1998, pp. 83-92).
However, because the impedance matching circuit 60 described above requires a relatively large occupation area as shown in FIG. 17 (for example, the occupation area is about 0.5 mm2 because it is 700 μm square, where L=57.5 nH and 2.4 GHz), there has been a problem that the ASIC is enlarged if the impedance matching circuit 60 is configured on the ASIC as it is. Still more, because the function of the impedance matching circuit 60 is limited to matching of impedance, i.e., it does not function as a filter, there has been a problem that a bandwidth cannot be set.
Accordingly, it is an object of the invention to provide an impedance matching circuit that allows a predetermined bandwidth to be set while allowing to be configured on a semiconductor element by reducing its occupation area and to provide a semiconductor element and a radio communication device using the same.